A critical approach to the toxic metal ion removal by hazelnut and almond shells.

The adsorption capacity of ground hazelnut (HS) and almond (AS) shells towards Pb(II) and Cd(II) has been studied at pH = 5, in NaNO3 and NaCl ionic media, in the ionic strength range 0.05-0.5 mol L-1. Kinetic and equilibrium experiments were carried out by using the Differential Pulse Anodic Stripping Voltammetry technique to check the amount of the metal ion removed by HS and AS materials. Different kinetic and equilibrium equations were used to fit experimental data and a statistical study was done to establish the suitable model for the data fitting. A speciation study of the metal ions in solution was also done in order to evaluate the influence of the ionic medium on the adsorption process. TGA-DSC, FT-IR, and SEM-EDX techniques were used to characterize the adsorbent materials. The mechanism of metal ions adsorption was explained on the basis of the results obtained by the metal ions speciation study and the characterization of materials.

Pb(II) adsorption by a novel activated carbon - alginate composite material. A kinetic and equilibrium study.

The adsorption capacity of an activated carbon - calcium alginate composite material (ACAA-Ca) has been tested with the aim of developing a new and more efficient adsorbent material to remove Pb(II) ion from aqueous solution. The study was carried out at pH=5, in NaCl medium and in the ionic strength range 0.1-0.75molL-1. Differential Pulse Anodic Stripping Voltammetry (DP-ASV) technique was used to check the amount of Pb(II) ion removed during kinetic and equilibrium experiments. Different kinetic (pseudo first order, pseudo second order and Vermuelen) and equilibrium (Langmuir and Freundlich) models were used to fit experimental data, and were statistically compared. Calcium alginate (AA-Ca) improves the adsorption capacity (qm) of active carbon (AC) in the ACAA-Ca adsorbent material (e.g., qm=15.7 and 10.5mgg-1 at I=0.25molL-1, for ACAA-Ca and AC, respectively). SEM-EDX and thermogravimetric (TGA) measurements were carried out in order to characterize the composite material. The results of the speciation study on the Pb(II) solution and of the characterization of the ACAA-Ca and of the pristine AA-Ca and AC were evaluated in order to explain the specific contribution of AC and AA-Ca to the adsorption of the metal ion.

Experimental and robust modeling approach for lead(II) uptake by alginate gel beads: influence of the ionic strength and medium composition.

Systematic kinetic and equilibrium studies on the lead ions removal ability by Ca-alginate gel beads have been performed by varying several internal parameters, namely, number of gel beads, nature and composition of the ionic medium and pH, which allowed us to model a wastewater in order to closely reproduce the composition of a real sample. Moreover, the effects brought about the different ionic species present in the reacting medium have been evaluated. Differential Pulse Anodic Stripping Voltammetry (DP-ASV), has been systematically used to perform kinetic and equilibrium measurements over continuous time in a wide range of concentration. Kinetic and equilibrium data have been quantitatively analyzed by means of robust approach both for the non-linear regression and the subsequent residuals analysis in order to significantly improve the results in terms of precision and accuracy. Alginate gel beads have been characterized by SEM and an investigation on their swelling behavior has also been made. Removal efficiency of the calcium-alginate gel beads has been calculated and results obtained have showed a relevant dependence on ionic strength, composition of ionic media, pH of solution and number of gel beads. The number of gel beads takes part as key crucial components, i.e., the higher the number of beads the greater the amount of Pb(II) species removed from the sample, the lower the time needed to reach the maximum removal efficiency of 90%.

Sequestering ability of some chelating agents towards methylmercury(II).

A study on the interactions between CH(3)Hg(+) and some S, N and O donor ligands (2-mercaptopropanoic acid (thiolactic acid (H(2)TLA)), 3-mercaptopropanoic acid (H(2)MPA), 2-mercaptosuccinic acid (thiomalic acid (H(3)TMA)), D,L-penicillamine (H(2)PSH), L-cysteine (H(2)CYS), glutathione (H(3)GSH), N,N'-bis(3-aminopropyl)-1-4-diaminobutane (spermine (SPER)), 1,2,3,4,5,6-benzenehexacarboxylic acid (mellitic acid (H(6)MLT)) and ethylenediaminetetraacetic acid (H(4)EDTA)) is reported. The speciation models in aqueous solution and the possible structures of the complexes formed are discussed on the basis of potentiometric, calorimetric, UV spectrophotometric and electrospray mass spectrometric results. For the CH(3)Hg(+)-S donor ligand systems, the formation of ML(1-z) and MLH(2-z) complex species is observed, together with a diprotonated MLH(2)(3-z) species for CYS(2-), PSH(2-) and GSH(3-) and the mixed hydrolytic one ML(OH)(-z) for TLA(2-) and MPA(2-). The dependence of the stability on ionic strength and on temperature is also analysed. In the other CH(3)Hg(+)-L systems (L = MLT(6-), SPER and EDTA(4-)), ML(1-z), MLH(2-z) and MLH(2)(3-z) complex species are formed, together with the MLH(3)(4-z) species for SPER, the mixed hydrolytic ML(OH)(-z) one for SPER and EDTA, and the M(2)L(2-z) for EDTA only. On the basis of the speciation models proposed, the sequestering ability of the ligands towards methylmercury(II) cation is evaluated. All S donor ligands show a good sequestering power (at 10(-11) mol L(-1) level, in the pH range 4 to 8) following the trend MPA(2-) < PSH(2-) < GSH(3-) < TLA(2-) < CYS(2-) < TMA(3-), while significantly lower is the sequestering ability of MLT, SPER and EDTA (at 10(-3)-10(-5) mol L(-1) level, in the pH range 4 to 8).

Absorption of polycyclic aromatic hydrocarbons by Pinus bark: analytical method and use for environmental pollution monitoring in the Palermo area (Sicily, Italy).

In the light of using biomaterial as pollutants sorbents for the environmental biomonitoring, we report here the results of the absorption of polycyclic aromatic hydrocarbons (PAHs) by pine bark. Quantitative analysis of 19 different polycyclic aromatic compounds was performed, after Soxhlet extraction in dichloromethane, by means GC-MS technique. Pinus was chosen due to its wide distribution in the Mediterranean area. The passive absorption of PAH by pine bark in the metropolitan areas allowed us to evaluate the air quality of Palermo. The obtained results showed a very high range of PAHs concentrations, from 33 microg/kg (bark dry weight), as SigmaPAHs, at the control site to 1015 microg/kg along a road with high traffic flow.

Sequestration of biogenic amines by alginic and fulvic acids.

The interaction of natural (alginic and fulvic acids) and synthetic (polyacrylic acid 2.0 kDa) polyelectrolytes with some protonated polyamines [diamines: ethylendiamine, 1,4-diaminobutane (or putrescine), 1,5-diaminopentane (or cadaverine); triamines: N-(3-aminopropyl)-1,4-diaminobutane (or spermidine), diethylenetriamine; tetramine: N,N'-bis(3-aminopropyl)-1,4-diaminobutane (or spermine); pentamine: tetraethylene-pentamine; hexamine: pentaethylenehexamine] was studied at T=25 degrees C by potentiometry and calorimetry. Measurements were performed without supporting electrolyte, in order to avoid interference, and results were reported at I=0 mol L(-)(1). For all the systems, the formation of (am)L(2)H(i) species was found (am=amine; L=polyelectrolyte; i=1...4, depending on the amine considered). The stability of polyanion-polyammonium cation complexes is always significant, and for high-charged polycations, we observe a stability comparable to that of strong metal complexes. For example, by considering the formation reaction (am)H(i)+2L=(am)L(2)H(i) we found log K(i)=6.0, 6.5 and 10.8 for i=1, 2 and 3, respectively, in the system alginate-spermidine. Low and positive formation DeltaH(degrees) values indicate that the main contribution to the stability is entropic in nature. The sequestering ability of polyelectrolytes toward amines was modelled by a sigmoid Boltzman type equation. Some empirical relationships between stability, charges and DeltaG(degrees) and TDeltaS(degrees) are reported. Mean values per salt bridge of formation thermodynamic parameters (DeltaX(degrees) (n)) are DeltaG(degrees) (n)=-5.8+/-0.4, DeltaH degrees (n)=0.7+/-0.5 and TDeltaS(degrees) (n)=6.5+/-0.5 kJmol(-)(1) for all the systems studied in this work.

Protonation of carbonate in aqueous tetraalkylammonium salts at 25 degrees C.

Protonation constants of carbonate were determined in tetramethylammonium chloride (Me(4)NCl(aq) 0.1Me(4)NCl>NaCl. An ion pair formation model designed to take into account the different protonation behaviours of carbonate in different supporting electrolytes was also evaluated.

Modelling of proton and metal exchange in the alginate biopolymer.

Acid-base behaviour of a commercial sodium alginate extracted from brown seaweed (Macrocystis pyrifera) has been investigated at different ionic strengths (0.1

Interaction of UO2(2+) with ATP in aqueous ionic media.

Interaction of dioxouranium(VI) (uranyl) ion with ATP was studied by ligand/proton and metal/hydroxide displacement technique, at very low ionic strength and at I=0.15 mol L(-1), in aqueous Me4NCl and NaCl solutions, at t=25 degrees C. Measurements were carried out in the pH range 3-8.5, before the formation of precipitate. Computer analysis allowed us to find the quite stable species UO2(ATP)H2(0), UO2(ATP)H-, UO2(ATP)2-, UO2(ATP)2(6-), UO2(ATP)2H2(4-) and UO2(ATP)(OH)3- whose formation constants are (at I=0 mol L(-1)) logbeta(112)=18.21, logbeta(111)=14.70, logbeta(110)=9.14, logbeta(120)=12.84, logbeta(122)=24.82, and logbeta(11-1)=2.09, respectively. Different values were obtained in the above ionic media at I=0.15 mol L(-1) and the dependence on the ionic medium was interpreted in terms of interactions between the negatively charged complex species and cations of supporting electrolytes. The species more stable in NaCl than in Me4NCl are those with the highest negative charge, UO2(ATP)2(6-) and UO2(ATP)2H2(4-), and the extra stability of these species can be attributed to the interaction with Na+. Speciation profiles show that ATP can suppress UO2(2+) hydrolysis, and that in the neutral to slightly alkaline range the yield of complex UO2-ATP species is quite high. Comparison with other metal-ATP systems is also given in order to recognize the possibility of binding competition of uranyl ion in metal-ATP requiring enzymes for biochemical processes.

Interactions of diethylenetriaminepentaacetic acid (dtpa) and triethylenetetraaminehexaacetic acid (ttha) with major components of natural waters.

The binding ability of diethylene triamine pentaacetate (dtpa(5-)) and triethylene tetraamine hexaacetate (ttha(6-)) ligands towards major components, H(+), Na(+), Mg(2+) and Ca(2+), of natural waters was studied in both single and mixed ionic media at different ionic strengths and at T=25 degrees C. Some measurements, performed in Mg(2+)-Ca(2+) mixtures, allowed us to find the formation of new mixed species MgCa(dtpa), MgCa(ttha) and MgCaH(ttha), here reported for the first time. All the complexes formed in the various systems were characterized in terms of both stoichiometry and stability, and an attempt was made to find general rules for the stability of mixed metal complexes in comparison with that of simple species. To obtain quantitative information on the complexing ability of dtpa and ttha in seawater, measurements have been carried out in artificial seawater ionic medium (Na(+), K(+), Ca(2+), Mg(2+), Cl(-) and SO(4)(2-)). Calculations, performed by considering the salt mixture as single salt BA, allowed us to find some quite stable B(i)H(j)L species. Under the natural seawater conditions [S(salinity)=35], we found for the most important species logbeta( B(dtpa))=9.64 and. Literature data comparison is also reported.

Quantitative parameters for the sequestering capacity of polyacrylates towards alkaline earth metal ions.

The complex formation constants of polyacrylic (PAA) ligands (1.4

Interaction of alkyltin(IV) compounds with ligands of interest in the speciation of natural fluids: carboxylate and hydroxycarboxylate complexes of monomethyltin(IV) trichloride.

The formation and stability of some carboxylate and hydroxycarboxylate (acetate, 1,2,3-propanetricarboxylate, 1,2,3,4-butanetetracarboxylate, malate and citrate) complexes of monomethyltin trichloride was studied potentiometrically at 25 degrees C and at different ionic strengths in NaNO3 aqueous solution. The following quite stable species are formed in the different systems (M = CH3Sn3+): ML(OH)+, ML2(OH)0, ML(OH)2(0) and M2L(OH)5(0) for acetate; MLH+, ML0, ML(OH)- and ML(OH)2(2-) for propanetricarboxylate; MLH2+, MLH0, ML-, ML(OH)2- and ML(OH)2(3-) for butanetetracarboxylate; ML(OH)0, ML(OH)2- and ML(OH)3(2-) for malate; ML0, ML(OH)-, ML(OH)2(2-) and ML(OH)3(3-) for citrate. Hydroxycarboxylate complexes are significantly stronger than simple carboxylate ones and this is likely to be due to the interaction of the -OH group in citrate and malate with monomethyltin(IV), whose strength was also quantified. It was found that the stability of these complexes can be roughly expressed by the simple relationship log K = a zeta, where zeta is the product of the charges of reactants and log K is the equilibrium constant. For simple carboxylic ligands we have a = 1.8 +/- 0.4 and, for hydroxycarboxylic ligands, a = 3.7 +/- 0.9. Other useful empirical relationships are reported. Moreover, hydroxycarboxylic complexes also play a prominent role in the speciation of monomethyltin(IV) under the pH conditions of interest for natural fluids.

Protonation and complex formation of 5-sulfosalicylate in NaCl, CaCl2 and MgCl2 aqueous media. Speciation in synthetic seawater.

The binding capacity of 5-sulfosalicylic acid (ssa) towards cationic macro-components of natural waters has been investigated in different ionic media (NaCl, MgCl2 and CaCl2 aqueous solutions) and in the ionic strength range 0 < or = I < or = 1 mol dm-3. In order to contribute to the speciation of this multi-sites ligand, measurements have been carried out also in a synthetic seawater (SSWE) containing the major components of seawater (Na+, K+, Ca2+, Mg2+, Cl- and SO4(2-)). Measurements have been performed by potentiometry ([H+]-glass electrode), at t = 25 degrees C. A critical analysis on the experimental and literature data is also given.

Speciation of polyelectrolytes in natural fluids Protonation and interaction of polymethacrylates with major components of seawater.

Acid-base properties of two sodium polymethacrylates (W=4000 and 5400 Da) were studied potentiometrically in aqueous solution at 25 degrees C. Measurements were made in different salt solutions: LiCl 0.1-1.5, NaCl 0.1-2, KCl 0.1-2, Et(4)NI 0.1-0.75 mol l(-1), and in artificial seawater in the salinity range 10